NICOSIA, Cyprus — With time running out until Cyprus’s devastated banks must reopen their doors to the public, Cypriot and European officials are scrambling to put in place a set of measures that would allow jittery depositors access to their savings while preventing many billions of euros from fleeing the country.

But the situation is now looking even worse than anticipated. Instead of the relatively modest decline of 3 percent that is built into the forecast that underpins the country’s international bailout package, many economists say that estimate will need to be revised sharply downward given the shock that the island’s small economy has endured from the extended closure of its banks.

The bailout package being put together by the troika of international lenders — the International Monetary Fund, the European Central Bank and the European Commission — will consist of about 10 billion euros ($12.9 billion) in loans for Cyprus itself. But the cost of bailing out the island’s two largest banks, Bank of Cyprus and Laiki Bank, is to be borne by the banks’ large, uninsured depositors.

At a news conference on Tuesday, the governor of Cyprus’s central bank, Panicos O. Demetriades, said that he expected big depositors at the Bank of Cyprus to get a “haircut,” or loss, of about 40 percent on their 14 billion euros in long-term deposits. In exchange, depositors will receive shares in a recapitalized bank.

But with many economists now estimating that the Cypriot economy will contract 5 percent to 10 percent this year, it could well be that the depositors will have to take a bigger loss so that the bank can free up cash to protect its rapidly deteriorating loan book.

At Laiki Bank, which is even worse off, about 4 billion euros of deposits will be put in a bad bank and are most likely to be wiped out as the bank is wound down.

Debt experts say that as painful as such a trimming may be, it still may not be enough to guarantee the viability of the Bank of Cyprus, given the state of the economy.

“If you are not hugely conservative with regard to valuing Bank of Cyprus’s assets, the bank will be insolvent in 12 months,” said Adam Lerrick, a sovereign debt specialist at the American Enterprise Institute in Washington.

As of the third quarter of 2012, problem loans for the bank were 22 percent of the total, one of the highest ratios in the euro zone. That figure will have grown significantly over the last several months, economists here say.

Adding to the sense of confusion enfolding the country’s financial sector, the chairman of the Bank of Cyprus resigned abruptly Tuesday after a showdown with Mr. Demetriades, the head of the central bank, and the finance ministry.

The bank chairman, Andreas Artemis, complained that the authorities rode roughshod over him and his board by moving unilaterally to sell off units of the bank in Greece and for planning to impose the devastating haircut on big depositors.

In a statement later in the day, the bank said Mr. Artemis’s resignation had not been accepted and “will only apply if not withdrawn within one week.”

The government is also struggling to come up with some form of capital controls in a bid to prevent too much money from draining from the banks and leaving the country. Given that more than 30 percent of the Bank of Cyprus’s 14 billion euros in long-term deposits belongs to foreigners — mostly Russians and Greeks — who would not hesitate to take their money out of the country, the restrictions on those funds are likely to be onerous, bankers say.

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“That money is going to stay there for a very long time,” said one person who has been involved in the discussions, but who requested anonymity because he was not authorized to speak publicly.

On Tuesday, the Cypriot central bank said it had appointed Dinos Christofides, a well-known local business executive, to act as special administrator for Bank of Cyprus. Mr. Christofides has long experience in auditing and advising major local and international companies.

Fitch Ratings said it was cutting its credit grades on Cypriot banks because of the losses imposed by the deal on senior creditors. Fitch said it was cutting its rating on Laiki to default, and its rating on Bank of Cyprus to restricted default, a grade Fitch said meant that the bank had experienced a payment default on a bond, loan or other material obligation but had “not entered into liquidation or ceased operating.”

And in London, George Osborne, the chancellor of the Exchequer, said his department was working with the Cypriot authorities to try to ensure that Laiki Bank’s branches in Britain — where the institution operates as Cyprus Popular Bank — were not entangled in the international bailout.

Beyond the challenge of dealing with the large depositors is the question of what to do with about 27 billion euros in deposits in accounts under 100,000 euros that now carry the Cypriot government’s full backing, following last weekend’s reversal of the decision to tax those deposits, too. That figure alone exceeds Cyprus’s annual gross domestic product of 18 billion euros.

If the banks reopen on Thursday, as planned, Cyprus’s shellshocked citizens will have access to their insured deposits for the first time in more than a week. With their bills and fears mounting, it is widely expected that many will immediately seek to remove these funds from the banks.

For now, officials say, it is likely that uninsured depositors will face stiff restrictions when it comes to withdrawing money from an automated teller machine or sending money abroad. But if a depositor at Bank of Cyprus wanted to transfer funds to, say, Hellenic Bank, a smaller institution that is in better shape, the controls would be less severe because that money would remain within the Cypriot banking system. Such arcane mechanisms are now being thrashed out in Brussels and Frankfurt.

Near the central square in Nicosia on Tuesday, Panayiotis Markou, 44, an employee of Bank of Cyprus, puffed on an electronic cigarette as he played cards with friends in the midday sun at a cafe called Kala Kathoumena, which loosely translates as “relax” in Greek. Mr. Markou warned that the forthcoming capital controls would set a dangerous precedent, in effect cutting off Cyprus from the rest of the 17-nation euro zone.

“Restrictions on currency means you have created two different currencies in the euro zone — a euro that is worth more and one that is worth less,” he said. “If you have 1 million euro in the bank but you can’t get it, it means that 1 million is effectively worthless.”

Horror stories abound here of flourishing local businesses that, because their deposits were kept at Bank of Cyprus or Laiki, are now on the verge of collapsing. It has all heightened anger toward decision makers in Brussels.

“We are facing an even deeper recession than the worst scenarios had predicted,” said Nicholas Papadopoulos, a member of the Cypriot Parliament and the chairman of the body’s financial committee. “We have become the Lehman Brothers of Europe.”

Correction: March 27, 2013

An earlier version of this article misstated part of a quote from Adam Lerrick of the American Enterprise Institute. He said, “If you are not hugely conservative with regard to valuing Bank of Cyprus’s assets, the bank will be insolvent in 12 months.” He did not say, “If you are not hugely conservative with regard to valuing Bank of Cyprus’s loans, the bank will be bankrupt in 12 months.”